1. Field of the Invention
The present invention relates to a composition for a resist underlayer film useful for a multi-layer resist process used in microfabrication in manufacturing of a semiconductor device and the like, to a process for forming a resist underlayer film using this, and to a patterning process using this, suitable for exposure by a far ultraviolet, a KrF excimer laser beam (248 nm), an ArF excimer laser beam (193 nm), an F2 laser beam (157 nm), a Kr2 laser beam (146 nm), an Ar2 laser beam (126 nm), a soft X-ray (EUV (Extreme Ultra Violet)), 13.5 nm), an electron beam (EB), and an X-ray, and the like.
2. Description of the Related Art
With highly integrated LSI's providing highly increased speeds, finer pattern rules are being rapidly promoted. Commensurately with the fineness, a lithography technique has attained formation of fine patterns, by virtue of light sources of shorter wavelengths and resist compositions appropriately selected therefor. The main role thereof was played by positive photoresist compositions to be each used as a monolayer. The monolayer positive photoresist composition is configured to possess, in a resist resin, a structure having an etching resistance against dry etching by chlorine-based or fluorine-based gas plasma, and to possess such a resist mechanism that an exposed portion is made dissolvable, so that the exposed portion is dissolved to thereby form a pattern, and the remaining resist pattern is used as an etching mask to dry etch a substrate to be processed coated with the resist composition.
However, when a pattern is made finer, i.e., pattern rules are further narrowed while keeping a thickness of a used photoresist film as it is, the photoresist film is deteriorated in resolution performance. Further, when the photo resist film is to be developed by a developer to form a pattern, a so-called aspect ratio thereof is made excessively large, thereby resultingly causing a pattern collapse. Accompanying the trend toward finer-pattern, the film thickness of a photoresist film has been made thinner.
Meanwhile, although for processing of a substrate to be processed, there is typically used a method for processing the substrate by dry etching by adopting a patterned photoresist film as an etching mask, practically no dry etching methods exist to exhibit a complete etching selectivity between a photoresist film and a substrate to be processed, so that the resist film is also damaged during processing of the substrate and the resist film is collapsed during processing of the substrate, thereby failing to accurately transfer a resist pattern onto the substrate to be processed. Thus, with finer patterns, resist compositions have been required to have higher dry etching resistances.
Further, since shortened wavelengths of exposure have demanded that resins having lower light absorption at exposure wavelengths are used for resist compositions, such resins have been subjected to a transitional history from a novolak resin, through polyhydroxystyrene, and to a resin having an aliphatic polycyclic frame, commensurately with a transitional history from i-line, through KrF, and to ArF. However, etching speeds under the dry etching condition have been practically made higher, so that recent photoresist compositions having higher resolutions practically tend to be rather lowered in etching resistance.
This obliges a substrate to be processed to be dry etched by a photoresist film which is inevitably thinner and weaker in etching resistance, thereby making it urgent to ensure a material and a process in this processing state.
As one of the methods for solving such problems, a multi-layer resist process is available. In this method, a intermediate layer film whose etching selectivity is different from that of the photoresist film, i.e., a resist upper layer film is disposed between the resist upper layer film and the substrate to be processed, the pattern is obtained in the resist upper layer film, subsequently the pattern is transferred onto the resist intermediate layer film by dry etching using the resist upper layer pattern as the dry etching mask, and further the pattern is transferred onto the substrate to be processed by the dry etching using the intermediate film pattern as the dry etching mask.
In a two-layer resist process which is one of the multilayer resist processes, for example, silicon-containing resin is used for the resist upper layer composition, and organic resin which has high carbon-containing volume, such as the novolak resin is used as the resist underlayer film. The silicon-containing resin exhibits the good etching resistance to the reactive dry etching with oxygen plasma, but is easily removed by the etching when fluorine-based gas plasma is used. Meanwhile, the novolak resin is easily removed by the etching in the reactive dry etching with the oxygen plasma, but exhibits the good etching resistance to the dry etching with the fluorine-based gas plasma and the chloride-based gas plasma. Thus, a novolak resin film is formed as the resist underlayer film on the substrate to be processed, and a resist upper layer film using the silicon-containing resin is formed thereon. Subsequently, the pattern is formed in the silicon-containing resist film by post treatments such as exposure to energy beam and development. Using this as the dry etching mask, the portion of the novolak resin where the resist pattern has been removed is removed by the reactive dry etching with the oxygen plasma to transfer the pattern in the novolak film. Using this pattern transferred to the novolak resin as the dry etching mask, the pattern can be transferred to the substrate to be processed using the etching with the fluorine-based gas plasma or the chloride-based gas plasma.
In such a pattern transfer by the dry etching, when the etching resistance of the etching mask is sufficient, the transferred pattern having a relatively good shape is obtained. Thus, a problem of a pattern collapse caused by friction and the like by a developer upon resist development hardly occurs, and the pattern having a relatively high aspect ratio can be obtained. Therefore, for example, when the resist film using the novolak resin has the thickness corresponding to the film thickness of the intermediate film, even in the fine pattern which could not be formed directly because of the pattern collapse upon development due to the aspect ratio, according to the above two-layer resist process, the novolak resin pattern having the sufficient thickness as the dry etching mask for the substrate to be processed is obtained.
The multi-layer resist process further include a three-layer resist process which can be performed by using a typical resist composition used in a monolayered resist process. For example, this method is configured to form: an organic film as a resist under layer film based on novolak or the like on a substrate to be processed; a silicon-containing film as a resist intermediate film, thereon; and a typical organic photoresist film as a resist upper layer film, thereon. Since the organic resist upper layer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist intermediate film for dry etching by fluorine-based gas plasma, the resist pattern is transferred to the silicon-containing resist intermediate film by means of dry etching based on fluorine-based gas plasma. According to this method, as well as two-layer resist process, patterns of novolak films having sufficient dry etching resistances for processing can be obtained insofar as patterns can be transferred to silicon-containing films, even by adopting: a resist composition which is difficult to be formed with a pattern having a sufficient film thickness for direct processing of a substrate to be processed; and a resist composition having an insufficient dry etching resistance for processing of a substrate.
While numerous techniques have been known (such as Japanese Patent Laid-Open (kokai) No. 2004-205685 and the like) for the organic underlayer film as described above, decrease of processing line width has been accompanied by such a problem that phenomena of twisting, bending, and the like of a resist underlayer film are caused when the resist underlayer film is used as a mask for etching a substrate to be processed (Proc. of Symp. Dry. Process, (2005), p 11). Such twisting of a fine pattern is considered to be caused by a phenomenon having been reported to result in substitution of hydrogen atoms of a resist underlayer film with fluorine atoms during etching of a substrate by a fluorocarbon-based gas, to thereby exemplarily increase a volume of the underlayer film to swell it and to lower a glass transition point thereof (Proc. of SPIE Vol. 6923, 692320, (2008)). In turn, it has been reported that the problem of twisting can be prevented by adopting an organic material, which is low in hydrogen atom content ratio, as a resist underlayer film. In this respect, amorphous carbon films formed by CVD are each allowed to be extremely less in the number of hydrogen atoms in the film itself, and are extremely effective for prevention of twisting. However, CVD is unfortunately insufficient in characteristic to fill up a height difference, which is present on a substrate to be processed, and it is occasionally difficult to introduce a CVD apparatus due to its cost and an increased footprint occupation area of the apparatus. It will be thus able to obtain a remarkable merit of simplification of a process and an apparatus, if the above problem of twisting is solved based on a resist underlayer film composition which can be formed into a film by coating, particularly by spin coating.
As the above-described film-forming material which is low in hydrogen atom content ratio and which can be coated and formed into a film, films each containing a fullerene derivative have been proposed for prevention of twisting up to now, which fullerene derivative is extremely high in carbon ratio. For example, while a method for forming a film by fullerene itself has been proposed at a very early stage (Japanese Patent Laid-Open (kokai) No. H06-61138), there have been subsequently and exemplarily proposed another method to once disperse a fullerene derivative into an organic resin and to cure the dispersion (Japanese Patent Laid-Open (kokai) No. 2004-264710, Japanese Patent Laid-Open (kokai) No. 2006-227391), a further method to form a fullerene derivative into a film and to cure it (WO2008/62888A1), and the like.
However, fullerenes each exhibit absorption over a range from visible to near-infrared light, as a nature of the applicable fullerene itself. As such, in case of a coated film containing a fullerene and/or fullerene derivative at a high concentration, it is likely to lose sight of an alignment mark to be used for alignment upon exposure process, thereby deteriorating an alignment precision. Further, it is possible to prevent twisting of a pattern, when etching is conducted based on a underlayer film formed of a composition, so as to prevent this problem, comprising: a fullerene and/or fullerene derivative; and a resin which is conventionally known to be less in light absorption in above-mentioned wavelength range. However, even in such a case, those compositions which result in considerable surface roughness of completed patterns are not practical, due to accompanying problems such as an increased probability of disconnection of resultant wiring, deterioration of parasitic capacitance, and the like. As such, composition control at a molecular level is demanded for a resist underlayer film-forming composition for forming an ultra fine wiring having a line width of 40 nm or less.